This invention relates to electromagnetically operated valves, and more particularly to an improved dual solenoid valve. Even more particularly, this invention relates to an improved three-way dual solenoid coil valve having three operational positions and the capability of operating in either pulse-width modulation or on/off mode.
Application of various solenoid valve types may be seen in anti-lock braking systems and the newer electronic transmissions. In such applications, the solenoid valves are employed to accomplish the task of obtaining intermediate pressure levels from a constant high pressure source The two way solenoid valve disclosed in U.S. Pat. No. 5,076,538, for example, utilizes an adjustment member interposed between the valve and the surrounding housing to delay or prevent the valve from moving suddenly from its closed to its fully open position. This causes a slight throttling of fluid pressure until the latter stabilizes somewhat between the fluid inlet and outlet ports, respectively.
One particular solenoid valve that is used with electronic transmissions comprises a three-way two-position valve such as the one disclosed in U.S. Pat. No. 4,932,439. This valve utilizes pulse width modulation (PWM) effectively to switch between a build phase where pressure is increasing at its outlet port and a decay phase where pressure is decreasing at its outlet port. Such two position valves have several disadvantages such as, first, difficulty maintaining desired pressures due to constant oscillation between build and decay phases, second, the necessity of a fast microprocessor the cost of which increases with efficiency, and third, rapid opening and closing of valves with generally metal-to-metal contact increases valve wear and diminishes durability.
Still another type of solenoid valve utilizes a linear or variable force to achieve regulation of the desired pressure Although less efficient than pulse-width modulation solenoids, these solenoids operate at high frequencies (e.g. 250 Hz.) such that the solenoid rarely allows complete valve closure, but rather causes varying restrictions in the flow rate from the high pressure source and to the low pressure exhaust. This limits the problem of oscillating pressures. However, these solenoid valves also have several disadvantages such as, first, calibration of these solenoid valves is difficult and timely to effect, and second, these solenoid valves tend to be very expensive to manufacture and operate.
Also used for electronic transmissions is a three way, three position pressure actuated directional valve of the type disclosed in U.S. Pat. No. 4,674,613. The directional valve is controlled by a solenoid operated relief valve having a single armature movable into three positions corresponding to the amount of voltage applied to its surrounding solenoid coil. The U.S. Pat. No. 3,783,901 also discloses a pressure actuated valve controlled by a solenoid-operated member, and although the solenoid includes two separate coils, the latter are utilized simply to make the solenoid double-acting.
It is therefore an object of this invention to provide a solenoid valve capable of three operating positions which render the system more efficient when regulating fluid pressures.
It is also an object of this invention to provide a solenoid valve whose moving parts oscillate less frequently and therefore, will wear more slowly, thereby rendering the valve more durable.
Another object of this invention is to provide a three position solenoid valve having its valving operation within the coil area, therefore reducing the space required by such an assembly.
Yet another object of this invention is to provide a dual solenoid valve which has two separate armatures disposed coaxially one within the other, and is therefore less expensive to produce and utilize.
Other objects of this invention will become apparent hereinafter from the specification and the recital of the appended claims, particularly when considered in conjunction with the attached drawings.